brick veneer on 4-story wood bldg

huangyhg

brick veneer on 4-story wood bldg
what are some opinions on supporting brick veneer with a wood backing? this building is around 45' tall with brick veneer. code seems to allow brick to span from the foundation upwards of 30' before needing a shelf angle. has anyone fastened a steel shelf angle to the exterior wall studs with lag bolts to support the masonry?
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i would discourage you from fastnening the shelf angle to the wood studs. wood has a rtendency to creep under sustained load and would likely affect the brick.
i am thinking that requirement was meant for high rise buildings.  attached to concrete or steel, the angles can actually support the brick, but lag bolted to wood studs?  i don't think so.  at any rate, i don't think the fire marshal would like it.  
i did a 4 story wood hotel and that same issue came up.  i checked the stresses in the masonry and they were fine.  the brick was installed all the way up only being braced back to the studs in the usaul manner all the gable ends and hasn't fallen down yet.  i think its been 7 or 8 years.
all that to say i am not sure if it is code compliant, but it will work.
so is supporting brick off of wood a bad thing to do, period?  
does that mean that if you have a wood building with brick veneer, you are always going to have all the brick supported at the foundation level?
what if, instead of having a shelf angle connected to woods studs, you had it tied into blocking or a double-top plate?
the code requirement to support brick vertically, has nothing to do with the stresses in the masonry, it has to do with the brick expanding vertically (due to moisture) and the structure not. this creates an incompatibilty that may cause significant problems with windows, window frames, joints,caulking, sealants, exterior and interior facades, etc.
the irc has details dealing with steel angles, attached to wood studs, and supporting brick masonry.  i've never liked it but its there none-the-less.
the ibc is explicit (in the anchored veneer section) that the brick should only go 30 feet in height where supplemental shelf angles are required.  i'm not sure that i would want brick veneer to be supported by wood structures in any case.   can you convince the architect to convert to eifs in the top story?
here is the way i see it (but not with 100% confidence):
1)  ibc 1405.5 says anchored veneer shall comply with aci 530, sections 6.1 and 6.2
2)  aci 530, section 6.1.2 says anchored veneer shall be designed rationally per 6.2.1, or by the prescriptive requirements of 6.2.2.
3)  6.2.2 (specifically 6.2.2.3.1.2) has a height limitation; 6.2.1 does not appear to limit the height.
4)  i have done a 4 story wood structure, with the brick veneer all supported on the foundation, and had no problems whatsoever.
in many areas, eifs is not permitted on wood frame structures. ok for concrete, masonry or steel.
if i were going to hang brick on a wood frame structure, i would have shelf angles every two floors at the most. - with appropriate details per code.
the differential length change between different materials takes place over time, so a 5 year or so time frame may not reveal any problems or provide a measure of acceptibility.
clay brick has an irreversible long term expansion. if you have concrete brick, the long term effects are for shrinkage, which is more compatible with structural materials under compression. concrete brick is not a large percentage of the brick used, but it is increasing.
wood is subject to creep/shrinkage so the long term dimensional differential can be appreciable over a long period. the biggest problems occurs at openinings on the upper (depends on distance above the veneer support). a similar situation exists for concrete structures, but not to the same degree.
dick
here is the response on this issue that we've recently recieved from aci; however, it doesn't sound to be etched in stone. i think more clarification is needed from the codes on this.
"section 6.2.2.3 of aci 530 regulates the vertical support of anchored masonry veneer. section 6.2.2.3.1.2 and table 6.2.2.3.1 limit the height of the veneer above noncombustible foundation. an exception is given for veneer with a backing of cold-formed steel backing, section 6.2.2.3.1.3. there are no restrictions on the height of veneer backed by concrete or masonry. this is a fire protection requirement. the designer should also consider the effects of differential movement on the anchors and connection of the veneer to other building components. see commentary section 6.2.2.3.
as this restriction is fire safety related, additional calculations would probably not be a sufficient proof for an alternative approach
sincerely,
technical staff"
i believe that i read that the vertical brick expansion is estimated to be about 1/10 of an inch in 10 feet. i would advise to apply for a variance. then if it is allowed, i would make sure that you isolate all windows, etc. and allow for that movement plus the axial shortening and long term creep of the wood studs plus some construction tolerance. as someone else pointed out, this is especially important at the top of the structure.